Yes, it's still illegal and the fine is pretty hefty. In Portugal, using your phone in your hand while driving is against the traffic code, and fines range around 120 to 250 euros, depending on whether it's a first offense or repeat violation. Plus, you lose points on your license (I think it's 3 points). The law hasn't changed on this, so if you get caught replying to messages while driving, yes, you can be fined.
The most important thing is to understand that this isn't just a legal issue - it's a safety issue, really. Divided attention at the wheel causes serious accidents, and authorities are cracking down on this more and more because they know the risk. There are alternatives that work well: if you really need to reply to something urgent, pull over somewhere safe, or use a phone holder with a hands-free kit to make calls (that's legal). If you're the type who gets a lot of messages during your drive, it might be worth turning on "Do Not Disturb" while you're driving.
Just curious: are those messages you need to reply to actually urgent, or is it more of a habit? If it's work-related, maybe it's worth talking to your boss about it, because it's not smart to risk a hefty fine (and your safety) over messages that can wait half an hour.